While new technologies and filters have removed the bulk of carbon particulates emitted from diesel exhausts, questions are now being raised about the chemical composition of what is left – tiny nano-particles that may or may not have adverse health effects.
Newer technology machines, including electronically controlled machines, along with a range of filtration devices, have removed what was thought to be the major problem – particulates - bringing many of these machines into statutory compliance.
All existing regulations, however, attempt to limit exposure by mass. They do not take account of number of particles or chemical composition of particles.
NIOSH has begun working on the characterization of the remaining diesel particulate matter coming out of engines that use modern emission control technology.
“The hypothesis is that the historical determination of the health risks from diesels was done on diesel machines that were 20-years-old where the diesel particulate particles are much larger and possibly of a different nature to what is coming out of modern technology engines today,” said George H Schnakenberg, research physicist, who heads the Diesel Team.
“Diesel machines with filters emit few to no solid particles, however there is an increased number of very small, or nano-particles, which are probably organic condensates. In removing the solid particles, the organic vapor has no host particle to attach themselves to so you end up with a saturated vapor of organic material.”
What is unknown is whether this vapor is potentially carcinogenic.
According to Schnakenberg, such small entities are known to penetrate deep into the lung and are able to pass through cell walls in animals and go directly into the body where they can cause health risks.
Diesel equipment testing has been started at NIOSH’s Lake Lynn laboratory facility, which is fitted with an engine dynamometer and emissions measuring devices.
This experimental underground mine facility is being geared up to capture nano-particles according to size so they can be analyzed by a variety of physical and chemical methods.
“We are seeking to provide toxicologists with a full spectrum of information so they can assess the difference between older exhaust and newer exhaust emissions,” Schnakenberg said.
“We do know the statement - diesel exhaust is a potential carcinogen - is based on studies of old technology.”
Another diesel project underway aims to make available clean, electronically controlled engines for use underground at high altitudes, particularly for Western coal mines.
NIOSH has been working with MSHA to develop approval protocols to allow the determination of ventilation rate of an engine by testing it in simulated high altitudes.
“Tests are traditionally conducted at sea level, a procedure that is adequate for mechanically controlled engines whose emissions can be predicted when fuelling rate is cut back for high altitudes, but with electronically controlled engines, pressure sensors control both fuelling rate and injection timing, resulting in an uncertainty in emissions at high altitudes,” Schnakenberg said.
High altitude, third-party test labs will probably be used (for engines up to 10,000ft) with the engines expected to gain approvals under the auspices of new technology.
Finally, the NIOSH Diesel Branch has done a lot of work on changing the surrogate for measuring diesel particulate matter from total carbon to elemental carbon. A proposed rule covering this has been released.